To compare the insecticidal activity of natural essential oils of citronella, mustard, sage, and their nanoemulsions against the second and fourth instar larvae of greater wax moth, Galleria mellonella, the tested natural oils were converted into nano emulsions that were formulated and bioassay evaluated. The results indicated that LC50 values were 0.266, 0.553, and 0.791% for mustard, citronella, and sage oils, respectively. While in case of mustard, citronella, and sage nanoemulsions LC50 values were 0.226, 0.501, and 0.238%, respectively when tested on the 2nd instar larvae. While on the 4th instar larvae the LC50 values were 5.944, 1.454, and 2.609% for mustard, citronella, and sage oils, respectively. On the other hand, LC50 values were 0.663, 0.504, and 0.700% for mustard, citronella, and sage nanoemulsions, respectively. These results proved that essential oils nanoemulsions were more effective than conventional oils. Biochemical changes induced in 4th instar larvae at the treatment with LC50 of tested essential oils and their nanoemulsions were also studied. According to the findings, all examined essential oils elevated the activities of acetylcholinesterase (AChE) and decreased the activity of glutathione S-transferase (GST) in all treatments except citronella nanoemulsion where it caused significant increase. In addition, there were significant decrease in the activity of alpha esterases enzymes for all treatments except sage nanoemulsion which increase the enzymes activity of the tested larvae compared with the control.